There is a disclosed technique to apply an independent component analysis for equalizing a filter characteristic with an acoustic transfer function of an echo even during doubletalk in which a microphone signal simultaneously includes the echo and the speech of a near-end user, and appropriately cancelling the echo (see Patent Literature 1, for example).
There is another disclosed technique to apply the normalized least mean square (NLMS) based on a nonlinear function including a dead zone and an over-corrected zone (see Patent Literature 2, for example).